Neuroanatomical aspects of mydriatic action of morphine in rats

S. Kamenetsky, R. Rabinowitz, G. Urca, A. D. Korczyn*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Morphine causes mydriasis in rats. In order to investigate whether this effect is due to direct inhibition of preganglionic pupilloconstrictor neurons in the Edinger-Westphal nucleus (EWN), we injected opiate agonists into the EWN in male albino Charles River rats. Bilateral stereotactic microinjections of morphine (10, 20, 30, 40 μg/side) inhibited spinal nociceptive reflexes and caused pronounced catalepsy, but had no effect on pupillary size. The powerful opiate agonist, fentanyl, also elicited analgesia and catalepsy, when given in doses of 5 and 10 μg/side, but no dose of fentanyl up to 10 μg/side induced mydriasis. Naloxone (10 μg/side), given into the EWN, effectively antagonized inhibition of the tail-flick response induced by subcutaneously administered morphine (30 mg/kg), but had no effect on the cataleptic and mydriatic actions of systemic morphine. These results indicate that, in the rat, morphine-induced mydriasis is not accounted for by a direct action on the EWN.

Original languageEnglish
Pages (from-to)405-413
Number of pages9
JournalJournal of Ocular Pharmacology and Therapeutics
Volume13
Issue number5
DOIs
StatePublished - Oct 1997

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